My Blackberry Pearl was recently out of Warranty, I was considering using it for future international travel. I called ATT and told them I was planning International travel and needed to unlock my phone. They placed me on hold and eventually came back and had the code.

The process they described on the phone was slightly flawed, I wanted to share the correct process;

4. Press M E O O 2 (On the Pearl this requires Alt-T = 2, once again no spaces) At this point you should be looking at a box asking for a code. Note: You are typically limited to 10 tries, don’t mess this up. If you don’t have a code don’t even try this.

5. Enter the code ATT (or other provider gave you), click the pearl to select Now where before the list said "Network Enabled" should now say "Network Disabled" and you are good to go.